Biomedical Engineering Reference
In-Depth Information
FIGURE 9.4
Example of T1 (left) and T2 (right) weighted MR images. There is an obvious difference in the
contrast between these images. The left image is preferred for image registration since it shows
more anatomical detail and hence establishes the basis for functional-anatomical correlation.
The first image in Figure 9.4 is T1-weighted and shows a high resemblance to
a histological section and, therefore, is the first choice to obtain images with
predominantly anatomical information. T2-weighted images (the second
image in Figure 9.4), however, are preferred in order to detect subtle pathol-
ogies because they exhibit changes in intensity in abnormal tissues, espe-
cially in brain images. In nonbrain imaging, many pathologies are detected
because of their abnormal intensity pattern or deviation from normal anat-
omy. In contrast to PET imaging, MRI monitors tumors by size and structural
changes rather than by metabolic activity.
3
With modern magnetic resonance imaging systems, multiple planes at arbi-
trary orientations can be acquired (transverse, coronal, sagittal, and oblique
orientation), permitting an optimal positioning of slices relative to a particular
organ or region of the body. This feature is not available with most of the other
imaging techniques like PET or CT, whose primary images come in transverse
orientation. Other orientations are available only by means of interpolation
and reslicing of the primary images. Another predominant feature of MR
images is their much higher resolution compared with PET images. This
allows highly detailed morphological information to be obtained.
9.4
Problems and Solutions in MRI-PET Registration
9.4.1
General Considerations for Accurate Registration
of MR and PET Images
In order to successfully perform MRI-PET registration, some specific features
of each modality should be borne in mind, since a number of requirements
for successful image registration procedures have to be considered. These
include, among others, good image quality (resolution, contrast, no artifacts)
